The present invention relates to light fibers that transport light by total internal reflection.
It is known that optically transmissive materials such as glass or polymers may be used as light fibers to propagate light by total internal reflection. Light fibers typically comprise a core, typically of an inorganic glass or a synthetic polymer, and an optional cladding layer over the core. The cladding material preferably has a lower index of refraction that the core material and confines light energy to propagate through the core by total internal reflection.
In some instances it is desirable to provide a light-emitting region along at least a portion of the side or lateral surface of a light fiber. In order to provide such a light-emitting region, it is known to place a series of cuts at an angle to a plane normal to the longitudinal axis of the light fiber along the length of the light fiber. The cuts form a series of reflecting surfaces which act to reflect at least a portion of the light transmitted through the fiber out of the lateral or side surface of the fiber. If the light fiber has an outer cladding material the cuts extend through the cladding and into the core of the light fiber. Clad polymeric light fibers having notches cut along their length are commercially available under the trade designation xe2x80x9cPOLY BRIGHTxe2x80x9d from Poly Optics Australia Pty. Ltd.
Light fibers may be used in the design of illumination devices for hard-to-reach areas in-and-around internal combustion engines and/or during automobile body repair. Typically, these devices include a light source (e.g., a flashlight or an AC light source) and a length of light fiber in communication with the light source such that light emitted from the light source impinges upon one end of the light fiber and is transmitted through the fiber. It is often desirable for the illumination device to emit both endlight (i.e., light emitted from the end of the light fiber) and sidelight (i.e., light emitted from the lateral surface of the light fiber). Since the illumination devices of the type described are used in demanding environments where they are repeatedly bent and/or twisted in order to reach a remote area for viewing, and may be soiled by oil or grease, a rugged light fiber that is capable of being repeatedly bent and/or twisted and one that is capable of being easily cleaned is desired.
The present invention provides improved clad light fibers having a light emitting region and a continuous outer cladding layer covering the lateral (i.e., sidewall) surface of the light fiber and the light-emitting region. The improved clad light fibers have increased durability and may be more easily cleaned than prior art light fibers of the type having a series of cuts or embossed notches that extend through the outer cladding. The present invention also provides a method of making the clad light fibers of the present invention and illumination devices comprising the clad light fibers of the present invention.
In one embodiment, the present invention provides a light fiber comprising:
(a) an elongate polymer core having an input end for receiving light from a light source, an output end for emitting light transmitted through the core, and a lateral surface (i.e., a sidewall) extending along the longitudinal axis of the core;
(b) a light-emitting region comprising at least one optical element that directs light traveling though the core out of at least a portion the lateral surface of the light fiber in a direction generally transverse to the longitudinal axis; and
(c) an outer cladding layer which extends continuously over the lateral surface of the core and the light-emitting region said cladding layer comprising a polymeric material having an index of refraction that is less than the index of refraction of the core.
In one embodiment of the light fiber, the light-emitting region comprises a series of two or more optical elements separated at a distance from one another along the longitudinal axis of the core.
Preferably, the core of the light fiber comprises a poly(alkyl acrylates) or poly(alkyl methacrylates) and the outer cladding comprises fluorinated ethylene-propylene. Optionally, the light fibers may have a jacket layer over the outer cladding layer to provide additional protection to the light fiber.
The light-emitting region may comprise optical elements regularly spaced along the longitudinal axis of the core or optical elements that are irregularly (i.e., unequally) spaced along the longitudinal axis of the core. The depth of the optical elements typically ranges from about 1% to about 10% of a thickness of the light fiber.
In another embodiment the present invention provides a method of making a light fiber having a light-emitting region comprising the steps of:
(a) providing a clad light fiber comprising an elongate polymeric core having an input end for receiving light from a light source, an output end for emitting light transmitted through the core, and a lateral surface (i.e., a sidewall) extending along the longitudinal axis of the core;
(b) providing an embossing tool having at least one embossing element; and
(c) embossing the light fiber by bringing into contact the embossing element of the embossing tool with the cladding layer of the light fiber and apply pressure such that the embossing element indents the core of the light fiber thereby forming an optical element;
wherein the cladding layer is not cut during the embossing step (i.e, step c) such that the cladding extends continuously over the lateral surface of the core and the light-emitting region.
In one embodiment of the method, a rotary embossing apparatus comprising an embossing wheel having a series of embossing elements spaced over the circumference of the wheel is employed. Embossing of the clad light fiber is achieved by rotating the wheel about its central axis while the embossing elements of the wheel are in contact with the lateral surface of the light fiber.
In another embodiment of the method, at least one embossing elements comprises a first side surface and a second side surface which meet to define a vertex having an angle ranging from about 20xc2x0 to about 150xc2x0. Preferably, the vertex of the embossing element is truncated or radiused to prevent the embossing element from cutting the cladding of the light fiber.
In yet another embodiment the present invention provides an illumination device comprising:
(a) a light source;
(b) a light fiber comprising:
an elongate polymeric core having an input end for receiving light from a light source, an output end for emitting light transmitted through the core, and a lateral surface extending along a longitudinal axis of the core between the input end and the output end;
a light-emitting region directing light traveling though the light fiber out of at least a portion the lateral surface of the light fiber in a direction generally transverse to the longitudinal axis, the light-emitting region comprising at least one optical element; and
a continuous outer cladding layer comprising a polymeric material having a lower index of refraction than the core extending over the lateral surface of the core and the optical elements;
wherein the light fiber is optically coupled to the light source such that at least a portion of the light emitted from the light source impinges on the input end of the light fiber.
The light fiber may be rotatably or non-rotatably connected to the light source. It may be preferable in some embodiments for the light fiber to be detachably connected to the light source. In this way, the light source may be used with other light fibers having, for example, a different lateral angular distribution of light. In one preferred embodiment the light source is a standard flashlight.
The term xe2x80x9clight-emitting regionxe2x80x9d refers to portions of a light fiber from which light propagating through the light fiber is emitted. The light-emitting region may extend along the entire length of the light fiber or it may extend along only a portion of the length of the light fiber. The light-emitting region may emit light with a lateral angular distribution of 360 degrees or less.
The term xe2x80x9coptical elementxe2x80x9d is used herein to encompass any controlled indentation formed in the core of the light fiber by an embossing process, which defines one or more reflecting surfaces capable of reflecting at least a portion of light impinging thereon through the wall of the fiber. Such optical elements are to be distinguished from scratches and other imperfections and other surface irregularities, which may occur from time to time in light fibers. By appropriate control of the size and shape of each optical element as well as the pattern and spacing of the elements along the fiber, light can be selectively emitted through the light-emitting region of the sidewall of the fiber.
The term xe2x80x9cillumination devicexe2x80x9d refers to devices that provide light with the desired wavelength(s), intensities, and distribution properties. Illumination devices may be portable or stationary.
The term xe2x80x9cworklightxe2x80x9d refers to an illumination device designed to illuminate areas during the performance of a task or tasks by a person, animal or machine (e.g., inspection via cameras or other sensors). A worklight may be portable or stationary.
The term xe2x80x9clateral angular distributionxe2x80x9d refers to the angle over which light is emitted from the light fiber as measured in a plane that is generally perpendicular to the longitudinal axis of the light fiber.
The term xe2x80x9clight fiberxe2x80x9d refers to an article that receives light at an input end and propagates light to an output end and/or a light-emitting region without significant losses. In general, light fibers operate on the principle of total internal reflection, whereby light traveling through the light fiber is reflected at the surfaces of the light fiber based on differences in the indices of refraction of the material of the light fiber and the material immediately surrounding the light fiber, for example, air, cladding, etc.
The term xe2x80x9cclad fiberxe2x80x9d is used to describe a fiber which consists of a core having a coating of a cladding material having a lower refractive index than the core material.
These and other features and advantages of the present invention will be described more completely below with respect to various illustrative embodiments of the invention.